Development of an irrigation controller mechanically actuated by soil-water tension

Keywords in English

Automation
Irrigation - Management
technological innovations

Abstract in English

The automation of irrigation scheduling is critical to maximizing water use efficiency and productivity in irrigated crops. However, the majority of automated irrigation controllers are electrically actuated and inappropriate for use by small-plot holders where there is no electricity. This research has developed and evaluated a mechanical irrigation controller actuated by soil-water tension for use by small-plot holders. The device uses the energy fluctuations inside a tensiometer located in the active root zone of the crop to mechanically actuate a switch valve which in turn operates the irrigation supply valve.The controller was designed and construced using readily available irrigation fittings and other components constructed in a lathe. It was constructed two prototypes, called prothotype I and II. The performance of six irrigation controllers from the prototype I and prototype II were evaluated in laboratory and in field experiments, respectively. The controller was able to turn on and off irrigation system both in field and laboratory conditions. However, variations (up to 5 kPa standard deviation) in the irrigation actuation and cut-off soil tensions were indentified between individual controllers. However, the calibration of either the actuation or the cut-off soil tension for individual controllers is possible and shown to reduce the variation between controllers to < 1 kPa for the calibrated function. Soil-water simulations were conducted using SWIMv2.1 model to evaluate the effect of sensor accuracy, soil type, irrigation application rate and the installation depth of the sensor on irrigation performance. The controller was shown to perform best when placed in depths bigger than 15 cm and soil-water activation bigger than 15 kPa. In the situation where more precision is required in the actuation of the irrigation system (irrigated crops with shallow root system) and/or is necessary more flexibility in the water depth to be applied, it is recommended utilize two controllers, one to turn on the irrigation and another to turn it off. The best application and soil water storage efficiencies were verified in controller placement depths between from 30 to 40% of the active root system of the crop.

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